@article{SM_2017_208_5_a0,
     author = {E. R. Avakov and G. G. Magaril-Il'yaev},
     title = {Relaxation and controllability in optimal control problems},
     journal = {Sbornik. Mathematics},
     pages = {585--619},
     year = {2017},
     volume = {208},
     number = {5},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_2017_208_5_a0/}
}